Railway road beds must be capable of supporting extremely heavy rolling stock. Railway road beds have traditionally included closely spaced railroad ties for supporting the railroad rails. The ties in turn are supported by ballast comprising debris free rocks through which rain water can quickly drain. It has long been recognized that drainage ditches running parallel to the railway road bed are necessary to carry away rain water that is drained from the railway road bed through the ballast.
The digging and maintenance of drainage ditches along a railway road bed can be a time-consuming process, and maintenance operations can obstruct portions of the railway to commercial rolling stock while the road bed is worked on. Rotary drum cutting heads have been used on machines for digging ditches or trenches along a railway road bed to increase the rate at which the ditch can be dug. Previous designs of rotary drum cutting heads, however, have required extremely large drums which must be mounted and used only on a given side of a railway mounted support carriage. Such ditch digging machines can dig a ditch only on one side of a railway road bed without transporting the support carriage to a turnabout area on the railway for reversing the orientation of the carriage on the railway.